1. Field of the Invention
The present invention relates to a Group III nitride semiconductor light-emitting device exhibiting reduced contact resistance between a p contact layer and an ITO electrode.
2. Background Art
In recent years, there has been an expanding demand for general illumination applications of Group III nitride semiconductor light-emitting devices, and high-power light-emitting devices are being developed. Every year, the driving current is increasing with the development of high-power light-emitting devices. Therefore, the power consumption is remarkably increased due to resistance, causing reduction in light emission performance. To avoid this, the resistance of light-emitting devices must be reduced.
Most of Group III nitride semiconductor light-emitting devices currently produced are of a lateral conductive face-up type or flip-chip type. In the face-up type device, an ITO transparent electrode is formed on almost the entire top surface of the p contact layer. In the flip-chip type device, a reflecting electrode of high-reflectivity metal such as Ag or its alloy is formed on almost the entire top surface of the p contact layer. To reduce the resistance of light-emitting devices, the contact resistance between the p contact layer and the electrode may be reduced. Improved light emission performance and uniform light emission distribution can be expected by reducing the contact resistance.
Japanese Patent Application Laid-Open (kokai) No. 2006-80469 or 2005-260245 discloses a method for reducing the contact resistance between a p contact layer and an electrode.
Japanese Patent Application Laid-Open (kokai) No. 2006-80469 discloses that a contact area with the p contact layer is increased by forming a concave and convex pattern on the top surface of the p contact layer. The concave and convex pattern can also improve the light extraction performance. The concave and convex pattern can be formed by crystal growth under the conditions that three-dimensional growth is dominant. The conditions that three-dimensional growth is dominant include growing at a low temperature, decreasing the hydrogen concentration in a growth atmosphere, increasing the Al composition ratio, and doping with Si. Alternatively, the concave and convex pattern may be formed by selective etching or selective growth.
Japanese Patent Application Laid-Open (kokai) No. 2005-260245 shows a Group III nitride semiconductor light-emitting device having a lattice-like metal layer on a p cladding layer, and a transparent ohmic contact layer formed of transparent conductive oxide on the p cladding layer and the metal layer. Such a structure can reduce the contact resistance.
However, even with the method disclosed by Japanese Patent Application Laid-Open (kokai) No. 2006-80469 or 2005-260245, the contact resistance between the p contact layer and the ITO electrode is not sufficiently reduced, and further reduction technique is desired.
The inventors of the present invention considered, from various experiment results, that high contact resistance between the p contact layer and the ITO electrode was caused due to lack of oxygen on an interface between the p contact layer and the ITO electrode. The present invention is derived from this consideration, and realizes a Group III nitride semiconductor light-emitting device exhibiting reduced contact resistance between the p contact layer and the ITO electrode by a method different from Japanese Patent Application Laid-Open (kokai) No. 2006-80469 or 2005-260245.